In the TDTT die prep process flow, a full thickness silicon wafer (approximately 700 micrometers (μm) thick) is mounted onto a semi-rigid backgrinding (BG) tape and thinned to some fraction of its original thickness. The thinned wafer with the BG tape is then sent to a backside metallization (BSM) module for sputtering deposition of a film stack typically comprising materials such as titanium (Ti), nickel-vanadium (NiV), and gold (Au). Because the glass transition temperature (Tg) of a BG tape is relatively low—approximately 90 degrees Celsius (° C.)—the thermal budget during BSM deposition must be carefully controlled.
During the thin-wafer BSM process, the wafer has to go through a low temperature degas process to remove surface moisture and then a sputter etch process to remove other remaining contaminations on the wafer surface. However, at wafer thinning a fresh silicon surface is exposed to the ambient environment and a thin native oxide layer is formed. During the sputter etch process, this native oxide layer will be removed easily and completely, resulting in a fresh silicon surface. Unfortunately, the adhesion of Ti to pure silicon is very poor, and the as-deposited BSM film stack will peel off in the downstream processes, i.e., saw, tape reel and die sort (TRDS), deflux, etc.
It is well known that the interface adhesion between Ti and silicon (Si) can be improved dramatically by forming Ti silicide. However, Ti won't react with Si to form Ti silicide unless it is exposed to a temperature above 600° C., which is incompatible with wafer backend and assembly processes. Accordingly, there exists a need for a method of forming a silicide layer (whether composed of Ti silicide or a different silicide, as determined according to the materials being used) that is compatible with the thermal budget of a TDTT process flow.
For simplicity and clarity of illustration, the drawing figures illustrate the general manner of construction, and descriptions and details of well-known features and techniques may be omitted to avoid unnecessarily obscuring the discussion of the described embodiments of the invention. Additionally, elements in the drawing figures are not necessarily drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve understanding of embodiments of the present invention. The same reference numerals in different figures denote the same elements.
The terms “first,” “second,” “third,” “fourth,” and the like in the description and in the claims, if any, are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in sequences other than those illustrated or otherwise described herein. Similarly, if a method is described herein as comprising a series of steps, the order of such steps as presented herein is not necessarily the only order in which such steps may be performed, and certain of the stated steps may possibly be omitted and/or certain other steps not described herein may possibly be added to the method. Furthermore, the terms “comprise,” “include,” “have,” and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements is not necessarily limited to those elements, but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.
The terms “left,” “right,” “front,” “back,” “top,” “bottom,” “over,” “under,” and the like in the description and in the claims, if any, are used for descriptive purposes and not necessarily for describing permanent relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in other orientations than those illustrated or otherwise described herein. The term “coupled,” as used herein, is defined as directly or indirectly connected in an electrical or non-electrical manner. Objects described herein as being “adjacent to” each other may be in physical contact with each other, in close proximity to each other, or in the same general region or area as each other, as appropriate for the context in which the phrase is used. Occurrences of the phrase “in one embodiment” herein do not necessarily all refer to the same embodiment.